SAE Review of Dr. Schneider's Paper, Part 3

Effect of Lubricant Properties and Lubricant Degradation on Piston Ring and Cylinder Bore Wear in a Spark-Ignition Engine, Schneider et al:

First read:
http://ferrarichat.com/forum/showthread.php?t=155529

Every person interested in motor oil should go to SAE.org and purchase this article. (The paper was very detailed and I have tried to simplify the results. Also, I will need to report the results in several different postings so hang on please.) This research is made more relevant by actually using V-6 engines for wear testing - 1999 GM 3.4-L 60 degree block. And the radiotracer method of wear detection has been shown to be very accurate. They go on to say that cylinder wear and ring wear are perhaps the best areas to test oil and wear for engine longevity, particularly the rings.

Part 3 and final in this review:

Fully formulated Synthetic SJ 0W-30, 5W-30 and SL 0W-30 oils were compared to SJ and SL 5W-30 mineral based oils for wear. There were no differences. (This is worth repeating - there were no differences in wear rates between mineral and synthetic based oils.)

Next are the effects of viscosity and oil temperature. Only ring wear was tested as they state it was most sensitive. They compared basic SJ GF-3 mineral oils. The additive packages were the same. The only difference was the viscosity of the base oils. The following grades resulted: 0W-10, 5W-20, 5W-30, 10W-40. The HTHS for these oils were 2.17, 2.83, 3.09 and 3.76.

There was no difference in wear rates. The oils were tested at all RPMs and Loads, no difference between oil grades were noted. All the oils had increasing wear rates as the load increased but all increased at the same rate across the board.

Most interesting to me was the way they tested wear at lower, start up, oil temperatures. In a previous study (1) they start with room temperature engines and oil showing the trend of decreasing wear as the engine heated up. In the current study they actually took a hot engine and chilled the coolant and oil from that of the normal operating temperature to a coolant temperature of around 80 F and oil temperature to 70 F. As the temperatures fell the wear increased. It reached the same rate of wear as the 4,000 RPM full load WOT. This was with the load at the minimum level. The fluids were then allowed to heat back up to normal operating temperatures and the wear rates normalized (decreased).

Wear at room temperature oil was 20 times higher than wear at normal operating temperatures. This finding is what closed the article. They stated that this will be the next focus of their upcoming research.

Final (personal) comments:

I like synthetic oils for very high temperature applications where the oil would consistently be above 260 F in the sump. I also like synthetic oils because they are less thick at start up at 70 F. These are worth the extra cost to me.

I like using slightly thinner oils when possible. I am not afraid of them. They allow for more BHP - get up and go. And you get a little better gas mileage. Why not take advantage of it if you can? Wear does not seem to be an issue much of the time.

aehaas

(1) Effect of Break-In and Operating Conditions on Piston Ring and Cylinder Bore Wear in SI (Spark-Ignition) Engines, Schneider et al:
The rate of wear is much higher within 15-20 minutes of start-up than after reaching normal operating temperature. There was a lot of data but I conclude that the initial start-up time period (first 20 minutes) result is 100 nanometers of wear whereas the steady state wear rate was only 4 nanometers per hour thereafter. (Hence we should be concerned about start-up oil thickness more than running thickness. This justifies the statement that 95 percent of engine wear occurs just after start-up.)